1. Technical Field of the Invention
The invention relates to recording and playback of signals from a magnetic tape. In particular, the invention relates to waveguide apparatus for coupling a high data rate signal to and from a rotary head scanner.
2. Description Relative To The Prior Art
A digital recording system must be capable of handling a very high data rate if a large volume of data is to be recorded in a relatively brief time interval. The need to enhance the data recording rate and packing density capability of a digital recorder of the rotary head scanner type places severe demands on existing methods for transferring the data signal to and from the magnetic head. Currently, the data signal to the rotary head is bandwidth limited by the commonly used rotary transformer to about 50 megahertz (50 MHz). The minimum bandwidth for a 300 megabit per second (Mb/sec) data rate, however, is 450 MHz, which, of course, is well beyond the frequency range of rotary transformers known in the art. Even with the introduction of electronics integral to a headwheel and improved transformer characteristics, rotary transformers known in the art. Even with the introduction of electronics integral to a headwheel and improved transformer characteristics, rotary transformers have a predicted upper bandwidth of only approximately 150 MHz. Accordingly, prior art digital recording apparatus suffers from a disadvantage in the inability to achieve the high data transfer rates required for currently proposed advanced digital recording systems.
Furthermore, it is desirable in the tape recording art to test and to certify that the tape recording system is accurately and reliably recording information. A high frequency, large volume recording system operating in real time requires a fast and efficient means of certification due to the cost involved in recording certain information, such as scientific data, which may not be repeatable. To date, playback, while simultaneously recording, has not been done satisfactorily with commercially available rotary head scanner apparatus.
U.S. Pat. No. 4,489,354 discloses rotary head scanner apparatus in which a stationary vertification head serves a monitoring function, checking continuously whether information to be recorded has actually been recorded. Although such a system has been found to work well for its intended purpose, it suffers from a disadvantage in that it fails to replicate the signals recorded, and thereby fails to provide information as to the quality of the recording.
In conventional rotary head scanner apparatus, the rotary transformer built into the scanner couples recording and playback signals to and from, respectively, rotating magnetic heads. A stationary part of a cylindrical assembly of the scanner contains the transformer primary; a rotating part of the assembly contains the transformer secondary. In recording, the stationary winding, as the primary, receives the signal, with magnetic coupling to the rotating secondary winding. In playback, the rotating winding acts as the primary coupling the signal into the stationary winding which acts as the secondary.
To simultaneously transfer multiple signals through a rotary transformer requires multiple coils on the rotating cores and multiple coils on the stationary cores. The distance between coils on the respective cores must be sufficient to avoid crosstalk between signals. Accordingly, in addition to the aforementioned bandwidth limitation of a rotary transformer, it is also difficult to simultaneously operate a rotary head scanner in both a record mode and a playback mode for a given size of rotary transformer.
It is known in the prior art that optical coupling of signals to and from a rotary head scanner offers potential advantages over a rotary transformer. Optical coupling permits broadband signal recording and reproduction with high efficiency and good signal-to-noise ratio; cross talk between multiple signals simultaneously transmitted can be virtually eliminated.
The aforementioned copending U.S. patent application Ser. No. 819,668, filed Jan 17, 1986 discloses rotary head scanner apparatus that is capable of bidirectional transfer of high fidelity signals contemporaneously. To that end, separate electro-optical data transmission channels serve, respectively, for routing a playback and a record signal between the stationary and rotating portions of the head scanner apparatus. Like rotary transformer apparatus for simultaneous bidirectional signal transmission, this arrangement also places restrictions on the size of the head scanner apparatus, because the uplink record channel and the downlink playback channel are required to be strategically placed at mutually exclusive points on the rotational axis of the headwheel.